Sinus Infection vs. Allergies: How to Tell the Difference

Disclaimer: This article is for educational purposes only and is not medical advice. If you have symptoms or health concerns, talk with a qualified clinician.

Congestion, a runny nose, and a foggy head — these symptoms can come from seasonal allergies or a sinus infection, and it is not always obvious which one you are dealing with. Getting the distinction right matters because the treatments are different.

This guide covers the key differences between allergic rhinitis and sinusitis, what to watch for, and when to see a healthcare provider.

Quick takeaways

• Allergies and sinus infections both cause nasal congestion and a runny nose — but the details differ.
• Itchy eyes and sneezing strongly suggest allergies; facial pain and fever point more toward infection.
• The color and consistency of mucus can be a useful clue (clear = more likely allergies; thick and colored = more likely infection).
• Sinus infections often follow a cold or allergy flare.
• Antibiotics are only appropriate for bacterial sinus infections — viral infections and allergies do not benefit from antibiotics.
• See a doctor if you are unsure, symptoms are severe, or you develop a high fever.

Understanding each condition

What are seasonal allergies (allergic rhinitis)?

Allergic rhinitis is an immune response to airborne allergens — most commonly pollen (from trees, grasses, and weeds), dust mites, pet dander, or mold. When you inhale these particles, your immune system releases histamine and other chemicals, triggering inflammation in your nasal passages and eyes.

Seasonal allergies follow pollen calendars. Perennial (year-round) allergic rhinitis is usually caused by indoor allergens like dust mites or pet dander.

What is a sinus infection (sinusitis)?

Sinusitis is inflammation of the sinuses — the air-filled cavities around your nose and eyes. It can be caused by:

• Viruses (most common — often follows a cold)
• Bacteria (less common; may require antibiotics)
• Fungi (rare; more common in immunocompromised individuals)
• Chronic inflammation from untreated allergies

Types of sinusitis:

• Acute sinusitis: Lasts less than 4 weeks; typically viral
• Subacute sinusitis: Lasts 4–12 weeks
• Chronic sinusitis: Lasts 12 or more weeks; may require specialist evaluation
• Recurrent sinusitis: 4 or more episodes per year

For an overview, see the AAO-HNS sinusitis resource.

Side-by-side comparison

Symptoms that point toward allergies

• Symptoms that start immediately or very soon after going outdoors
• Clear, watery nasal discharge that persists throughout the season
• Itching — nose, eyes, throat, or roof of mouth (a classic allergy sign)
• Sneezing fits, especially in the morning
• Red, watery eyes (allergic conjunctivitis)
• Symptoms that match a known pollen season or allergen exposure
• Symptoms that improve with antihistamines or intranasal corticosteroid sprays

Symptoms that point toward a sinus infection

• A cold that is not improving after 7–10 days, or gets worse after initial improvement
• Thick, colored (yellow or green) mucus
• Facial pressure or pain — especially in the forehead, around the eyes, or cheeks
• Reduced or absent sense of smell
• Fever (more common in bacterial sinusitis)
• Dental pain in the upper teeth (from pressure on the maxillary sinuses)
• Congestion that does not respond to typical allergy medications

The overlap: when allergies lead to sinusitis

This is where it gets tricky. Untreated or poorly controlled allergies can lead to sinusitis. When the nasal passages are chronically inflamed from allergies, mucus does not drain properly — creating conditions where bacteria or viruses can take hold.

Signs that an allergy flare may have become a sinus infection:

• Symptoms that were improving but suddenly worsen or plateau
• Fever develops during what seemed like an allergy flare
• Discharge changes from clear to colored
• Facial pain or pressure develops
• You feel significantly worse than during typical allergy symptoms

What can help (overview)

For seasonal allergies

• Intranasal corticosteroid sprays — often considered first-line for nasal symptoms; most effective with consistent daily use
• Oral antihistamines — second-generation options (cetirizine, loratadine, fexofenadine) are commonly used with less drowsiness
• Allergen avoidance — check pollen counts, keep windows closed, shower after being outdoors
• Saline nasal rinses — can help clear mucus and allergens from nasal passages
• Allergen immunotherapy — a longer-term option that may reduce allergic sensitivity

For viral sinus infections (most sinus infections)

Most acute sinus infections are viral and resolve on their own within 7–10 days. Antibiotics do not help viral infections.

Supportive care:

• Saline nasal irrigation (neti pot or squeeze bottle)
• Steam inhalation and warm compresses on the face
• Decongestants (short-term) — may relieve congestion
• Pain relievers (acetaminophen or ibuprofen) for facial pain and fever
• Rest and adequate hydration

For bacterial sinus infections

Bacterial sinusitis is less common (approximately 2–5% of sinus infections). Signs that suggest bacteria may be involved:

• Symptoms lasting more than 10 days without improvement
• High fever (above 39°C / 102°F) with severe facial pain
• "Double worsening" — initial improvement followed by significant worsening

A clinician may prescribe antibiotics if bacterial sinusitis is suspected. Do not request antibiotics for sinus infections unless a clinician determines they are appropriate — antibiotic overuse contributes to resistance.

For chronic sinusitis

Chronic sinusitis (lasting 12 or more weeks) may involve:

• Extended courses of intranasal corticosteroids
• Evaluation for structural issues (nasal polyps, deviated septum)
• Allergy testing and treatment
• Referral to an ENT specialist
• In some cases, functional endoscopic sinus surgery (FESS)

When to see a doctor

See a healthcare provider if:

• You have severe facial pain or headache
• Fever above 38.5°C (101.3°F)
• Symptoms are not improving after 7–10 days, or worsen after initial improvement
• You have changes in vision, swelling around the eyes, or a severe headache (these can indicate rare but serious complications — seek care promptly)
• You are unsure whether you have allergies or a sinus infection
• Symptoms have lasted more than 12 weeks (possible chronic sinusitis)
• You have had multiple sinus infections per year
• Symptoms are significantly affecting your quality of life or sleep
• You are immunocompromised, pregnant, or have other conditions requiring special consideration

Seek urgent or emergency care if you develop a high fever with stiff neck, visual changes, swelling around the eye or forehead, or severe headache — these may indicate rare but serious complications.

Getting the right diagnosis

A clinician can evaluate your symptoms and help determine the cause. This may include:

• Physical exam — checking nasal passages, throat, and lymph nodes
• Nasal endoscopy — direct visualization of nasal passages (performed by ENT specialists)
• Imaging (CT scan) — typically reserved for complex or recurrent cases
• Allergy testing — skin prick test or blood test to identify specific allergens

Knowing your triggers allows for targeted treatment, whether that involves managing allergen exposure, immunotherapy, or addressing structural factors.

Related reads

• Seasonal Allergies: Symptoms, Causes, and When to See a Doctor
• Contact Dermatitis: Triggers, Symptoms, and Relief

References

• American Academy of Otolaryngology — Head and Neck Surgery (AAO-HNS). Sinusitis: https://www.enthealth.org/conditions/sinusitis/
• American College of Allergy, Asthma & Immunology (ACAAI). Sinus Infection: https://acaai.org/allergies/allergic-conditions/sinus-infection/
• Centers for Disease Control and Prevention (CDC). Sinus Infection (Sinusitis): https://www.cdc.gov/antibiotic-use/sinus-infection.html
• Asthma and Allergy Foundation of America (AAFA). Sinusitis: https://www.aafa.org/sinusitis/
• American Academy of Family Physicians (AAFP). Sinusitis Overview: https://www.aafp.org/pubs/afp/issues/2016/0101/p30.html
• MedlinePlus. Sinusitis: https://medlineplus.gov/sinusitis.html
• NIAID. Allergic Rhinitis: https://www.niaid.nih.gov/diseases-conditions/allergic-diseases